Coaxial magnetron in which the anode is welded to the body



Nov. 19, 1968 K. D. POWELL" COAXIAL MAGNETRON IN WHICH THE ANODE IS WELDED TO THEBODY Filed Oct. 15, 1965 United States Patent 3,412,283 COAXIAL MAGNETRON IN WHICH THE ANODE IS WELDED TO THE BODY Kenneth D. Powell, Lancaster, Pa., assignor to Westinghquse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 15, 1965, Ser. No. 496,350 4 Claims. (Cl. 315--39.77)

ABSTRACT OF THE DISCLOSURE A coaxial magnetron structure in which the main assembly components of the magnetron are assembled and secured by welding techniques.

This invention relates to magnetrons and more particularly to coaxial cavity type magnetrons.

In the R. J. Collier et a1. Patent No. 2,854,603 issued Sept. 30, 1958, there is disclosed a coaxial magnetron structure which is comprised of inner and outer resonant systems. The inner resonant system, sometimes referred to as a vane and slot system, includes a cylindrical anode together with a plurality of anode vanes radially extending inwardly therefrom. These vanes define a circumferential array of inner, anode cavity resonators. The outer resonant system is a cavity resonator defined between an outer wall and the cylindrical anode. The inner and outer systems are coupled together by a circumferential array of spaced slots through the cylindrical anode which connects the outer resonant system with selected anode cavity resonators of the inner system. These coupling slots are normally made to extend axially beyond the limits of the inner anode resonators. The inner resonant system is designed to oscillate in the pi-mode while the outer resonant system is designed to oscillate in the TE u mode.

One general problem which industry faces in design of a magnetron for airborne applications is reducing the size and weight of the magnetron.

Another problem is to provide a design in which brazing is not required for secured the anode to the magnetron.

Many other problems face the designer and it is, accordingly, a general object of this invention to improve the design and manufacturing techniques of a coaxial magnetron.

It is another object of this invention to provide an improved coaxial magnetron of reduced weight and size over prior art.

It is another object to provide an improved structure for adjusting the match between the coaxial magnetron and the output waveguide system.

It is another object to provide an improved method of assembling and fabricating a magnetron.

It is still another object to provide an improved means of damping undesired modes of oscillation.

In brief, the present invention provides a compact coaxial magnetron configuration in which the main assembly components of the coaxial magnetron are assembled and secured by welding techniques. Other features of the invention are providing suitable attenuation of the TE coaxial mode within a minimum space and improved matching provisions between the output waveguide system to the coaxial magnetron.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularly in the claims annexed to and forming a part of the specification.

3,412,283 Patented Nov. 19, 1968 For a better understanding of the invention reference may be had to the accompanying drawings, in which:

FIGURE 1 is a side elevational view, partly in section;

FIG. 2 is a sectional view taken along the line II--II of FIG. 1;

FIG. 3 is a sectional view taken along the line IIIIII of FIG. 1; and

FIG. 4 is a partial view of the input window of the coaxial magnetron.

With reference now to the drawings, there is shown a coaxial magnetron embodying the present invention. The magnetron is comprised of a body member 10' which is substantially cup-shaped and includes substantially a cylindrical side wall 12 and a bottom end plate 14 of suitable electrically conductive material, such as copper. A welding termination lip 16, cylindrical in shape, extends from the lower surface of the bottom plate 14. Heat radiating fins 18 extend from a portion of the outer surface of the cylindrical side wall 12. An annular upper end plate 20 is provided on the upper portion of the cylindrical side wall 12 for closing off the body member 10. An aperture is provided in the upper end plate 20 through which an upper pole piece 22 projects into the interior portion of the body member 10. The upper pole piece 22 is annular in shape and a central opening therein provides means of exhausting the body member 10 and also surrounds the upper end of a cathode 24. An aperture or window 26 is provided in the cylindrical side wall 12 for extracting energy from the body member 10. A window assembly 30 associated with the output aperture 26 will be described in detail later. The above-described parts may be assembled as a unit and brazed at desired locations to provide a first unitary structure. I

The lower end plate 14 of the anode body 12 is also provided with an aperture and into which a second unitary assembly consisting primarily of an anode 32 and a third unitary structure consisting primarily of a lower pole piece 34 and cathode 24 are inserted.

The anode 32 which is also of a good electrical conductive material such as copper consists of a cylindrical anode wall 36 with a plurality of vanes 38 extending radially inwardly therefrom. The planes of the anode vanes 38 are inclusive of the axis of the cylindrical anode 32 and define in cooperation with the anode an array of anode cavity resonators 40. Coupling slots 42 extend through the cylindrical anode wall 36 and are centered between adjacent anode vanes 38. The coupling slots 42 communicate with alternate ones of the cavity resonators 40. The cylindrical anode 32 is inserted through the aperture in the lower end plate 14 and is seated against the upper pole piece 22 as indicated in the drawings. The lower end portion of the anode cylinder 36 is provided with an outturned flange 44 and a downturned flange or lip 46. The lip 46 is adjacent the lip 16 of the body 10 and provides a welding portion. When the anode 32 is inserted into the body member 12, the flange portion 44 is seated against the lower portion of the end plate 14 and the welding portion 46 is in engagement with the welding portion 16 of the body member 10.

Prior to insertion of the anode 32 into the body member 10, three annular members are slipped over the cylindrical side wall 36 including a spring member 50, an attenuator 52 and a matching ceramic 54. An annular grove 51 is provided in the wall portion of the aperture provided in the end plate 14 to position these three cylindrical members 50, 52 and 54 so that when the anode 32 is mounted to the body member 10 the two members 52 and 54 are spring loaded between the lower surface of the end plate 14 and the upper surface of the flange 44 of the anode 32.

The next assembly operation is the positioning of the cathode 24 and the lower pole piece assembly 60 into the magnetron. This unitary assembly is assembled prior to insertion into the body member 10. The assembly 60 consists of the lower pole piece 34 of a suitable magnetic material with the sleeve 62 of the cathode 24 extending through an aperture in the pole piece 34. The cathode 24 includes an electron emissive coating 64 secured to the cathode sleeve 62 in the region defined by the vanes 38 of the anode 32. The pole piece 34 is secured at its lower end to an insulating bulb portion 66. The bulb portion 66 is provided with a vacuum tight seal at the lower end thereof. A re-entrant portion 68 extending from the seal region includes terminals 70 and 72 for applying heating current to a heater provided within the cathode sleeve 62. A mounting plate 74 surrounds the lower end of the pole piece 34 for mounting the magnetron. A mounting block 76 is secured to the mounting plate 74 and the body portion 10. A collar member 80 is secured to the outer portion of the pole piece 34 as shown and is provided with a welding portion 82 which is seated within the flange portion 44 of the anode 32. These three welding portions 16, 46 and 82 may be welded so as to assemble the magnetron. This weld may be accomplished by a non-consumable electrode inert gas fusion welding using a suitable inert gas, such as argon. The envelope may then be exhausted through the port provided in the pole piece 22 and sealed off in a conventional manner.

In this manner, a brazing operation is not required to secure the anode 32 to the magnetron assembly which has the disadvantage of softening the work hardened anode causing dimensional instability and difliculty in salvaging of the magnetron. The welding is accomplished without subjecting the anode to high brazing temperatures. The assembly operation also has the advantage that cold tests can be made on the final assembly prior to welding and no changes will occur in the dimensions of the magnetron when the weld is made. The configuration also has the advantage that the copper to copper weld provided by the welding terminations 16, 46 and 82 provide a good thermal path from the anode 32 to the heat radiators 18. The assembly operation also permits the inside diameters of the annular pole pieces 22 and 34 to be smaller than the electron emissive coating 64 provided on the cathode to permit a more effective magnetic field with smaller dimensions. The weld also permits the magnetron to be easily opened up for repair without destroying the rest of the magnetron.

Encompassing the cylindrical anode wall 36 is the groove portion 51 within the bottom plate 14. An annular opening 90 within the bottom plate adjacent the anode wall 36 having a width of about .010 inch couples undesired modes into an annular groove 51. The groove 51 has a width of about .125 inch. The depth of the groove 51 from the upper surface of the bottom plate is about .150 inch. As previously mentioned, the groove 51 contains a matching ceramic ring 54 adjacent the entrance groove 90 which matches the TE coaxial mode field to the attenuator ring 52. The thickness of the ceramic ring 54 is optimum at slightly more than A8 in the dielectric about .035 inch for the Q-band. One prior design required intimate contact of the attenuator ring 52 to the body and the anode 32 to assure sufficient damping of the interfering TE mode. The prior art design was found to be very critical and difficult to achieve in production design. The arrangement illustrated herein permits a i005 inch tolerance on the ceramic length and still keep the damping of the TE mode below specifications. Another prior design used a slot to match the TE mode field to the attenuator. The slot is required to be approximately M4 in a vacuum. This prior design performs satisfactorily but takes considerable space. A suitable spring 50 of a material such as molybdenum is used to insure good contact of the matching ceramic ring 54 to the body 10.

A suitable material for the member 54 is high alumina ceramic and a suitable material for the member 52 is a high alumina content porous material loaded with carbon.

Referring now to the window design, the output energy from the megnetron is coupled through an output slot 26 into a rectangular waveguide 100. The rectangular waveguide is coupled through a circular waveguide 102 which is in turn coupled to a rectangular waveguide 104. A ceramic window 106 is sealed within the section of circular waveguide as indicated. The normal practice is to adjust the diameter and thickness and the circular waveguide length of the ceramic window 106 until a match over the desired band of operating frequencies is obtained. In this invention, the final match is achieved by the use of capacitive irises of each of the circular to rectangular waveguide junctions. Specifically, these irises are provided by the wires 108 provided along the long dimension of the waveguides and 104. The frequency of optimum match can be adjusted over a considerable frequency range with the same basic design. In the example of the Q-band magnetron, the window center frequency can be easily adjusted from 12 to 18 gc., the entire Q-band by changing the capacitive irises. This can be accomplished with different diameter wires brazed to the waveguides. The capacitive irises protect the window from damage due to arcing in the waveguide. The irises provide a breakdown point lower than at the window. This type of window design provides a very compact arrangement and in addition permits the thickness of the ceramic window to be set to a given thickness about 2 percent of A in air for proper strength without regard to adjusting the thickness to compensate for matching.

While there have been shown and described what are presently considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as wall within the true spirit and scope of the invention.

I claim as my invention:

1. A coaxial magnetron comprising a cylindrical anode wall member, a plurality of vanes extending inwardly from said anode wall and defining a plurality of anode cavity resonators within said anode wall member, said anode wall member having a downwardly turned welding flange portion, a cathode positioned within said anode wall member, the outer surface of said anode wall member defining one wall of an output cavity resonator, said output cavity resonator coupled to openings in said anode wall member to said anode cavity resonators, said outer cavity resonator including a lower end wall, said lower end wall having a downwardly extending welding flange portion thereon adjacent said welding flange portion of said anode wall member, a lower magnetic pole piece [member extending up through the lower portion of said anode wall member, said lower pole piece member having a downwardly extending welding flange portion extending from the outer periphery thereof and positioned in proximity to said welding flange portions of said anode and said end wall.

2. A coaxial magnetron comprising a body portion having a lower end wall, said lower end wall having a welding flange portion, a cylindrical anode member positioned within said body member and having a welding flange portion positioned adjacent said welding flange portion of said body member, a cathode positioned within said anode member, a coaxial cavity resonator surrounding said anode member, said anode member having slots therein for coupling energy from the inner portion of said anode member to said coaxial cavity resonator, a lower pole piece extending through a centrally located aperture in said end wall into said body member, said pole piece having a welding flange portion adjacent said welding flange portion of said anode, said welding flange portions being welded together by fusion welding.

3. A coaxial magnetron comprising a cylindrical anode wall, a plurality of radially extending vanes secured to said cylindrical anode wall and defining a plurality of anode resonators, said anode wall defining one wall of a coaxial cavity resonator, a cathode positioned within said anode wall, said anode wall including a plurality of openings for coupling energy from said anode resonators to said coaxial cavity resonator, an end cover member defining another wall of said cavity resonator and in contact with said anode wall and welded to said anode wall, the surface of said end wall having an annular gap adjacent said anode wall communicating with a groove portion beneath the surface of said end wall, said groove portion having a matching dielectric member in contact with said end cover and said anode for coupling energy through said annular gap, an attenuator ring in contact with said ceramic ring, said attenuator ring containing lossy material and a spring member for urging said attenuator ring and said matching ceramic ring against the lower surface of said groove within said end cover member.

4. A coaxial magnetron comprising a cylindrical anode wall member, a plurality of vanes extending inwardly from said anode wall member and defining a plurality of anode cavity resonators within said anode wall member,

wall member, a lower pole piece member extending up,

through the lower portion of said anode wall member and including an adapter ring about its outer periphery having a downwardly extending welding flange portion thereon positioned in proximity to said welding flange portions of said anode and said end wall to permit welding said anode, said end wall and said adapter ring in one operation.

References Cited UNITED STATES PATENTS 2,854,603 9/1958 Collier et a1. 315--39.77 3,034,014 5/ 1962 Drexler 315-39.77 3,325,671 6/1967 Biechler et a]. 3155.39

HERMAN KARL SAALBACH, Primary Examiner. S. CHATMON, JR., Assistant Examiner. 

